The use of electrostatic fields to separate hydrocarbon continuous emulsions or dispersions into organic and aqueous phases is well known in the separations industry. In the petrochemical or petroleum industry, electrostatic emulsion or dispersion separation is widely used in desalting crude oil before refining. Certain types of salts in crude oil are particularly detrimental to refinery equipment. Thus, the removal of impurities in crude oil is an important concern to the petroleum industry.
Desalting crude oil entails the formation of water-in-oil emulsions or dispersions by mixing a small quantity of water with a crude oil feed, usually at 4 to 10 percent of the crude oil feedrate, and then resolving the two-phase mixture in a vessel referred to as a "desalter." Impurites in the crude oil migrate to the entrained water droplets of the emulsion during such interaction. The water droplets eventually coalesce to form a distinct aqueous layer thereby providing a desalted crude oil layer ready for subsequent refining. However, to increase the rate of coalescence, desalters are normally equipped with electrodes to apply an electric field across the emulsion to polarize the water droplets.
Desalting apparatuses, including electrostatic desalters, require considerable capital expenditure. This is primarily due to their large size necessitated by the quantities of crude oil being desalted before refining can be commenced. Accordingly, considerable attention has been directed to improving the efficiency of petroleum desalters. One approach to increasing the efficiency of desalting operations is by using chemical additives such as demulsifiers and other desalting aids. Others have attempted to increase the efficiency of desalting operation by altering the design of the electrode assembly, the design of the desalter vessel, or both. While such attempts have improved the efficiency of desalting operations, there is still a continuing need in the art for increased efficiency levels due to the large quantities of crude oil that must be refined to satisfy current energy needs.
Accordingly, it is an object of the present invention to provide a method of increasing the efficiency of electrostatic emulsion or dispersion separation processes. In particular, it is an object of the present invention to provide a method of enhancing the coalescence rate of electrostatic desalting operations.